Twenty to thirty years ago cooling of residential and business establishments in warm arid or semi-arid climates was accomplished by means of evaporative coolers. These coolers rely upon the cooling effect obtained from moving a relatively dry air stream across water saturated pads to cool the air stream which then is supplied to the interior of the building to be cooled. Typically, the air exhausted from such a building has been exhausted through open doors and windows, since evaporative cooling systems do not employ recirculating air. Evaporative coolers are very effective during periods when the relative humidity is low and the ambient temperature is relatively high. Such coolers are relatively inexpensive to operate, since they require power only for operation of a blower or fan and require relatively modest amounts of water.
As the humidity increases, however, evaporative coolers become less effective and produce a damp clammy feeling to the inhabitants of a dwelling or building if the coolers are used on days having relatively high humidity.
Upon the development of relatively efficient and relatively inexpensive refrigeration systems, evaporative coolers steadily have been replaced with such refrigeration units over the past twenty to twenty-five years. In fact, most new construction in warm, semi-arid climates has included refrigeration units exclusively with very little new construction utilizing evaporative coolers.
Recently, however, energy costs have escalated considerably; so that renewed interest in evaporative cooling has taken place. An ideal solution to overcoming the shortcomings of both evaporative coolers and refrigeration units, appears to be to use both types of units, operating one or the other in accordance with the temperature and humidity conditions existing on any given day. For example, if the humidity is high, the refrigeration unit is operated to cool the building. If the humidity is low, the most efficient cooling of the building space is accomplished by the evaporative cooler.
Two patents which are directed to original equipment combination refrigeration and evaporative cooling air conditioner units are U.S. Pat. Nos. 3,182,718 and 3,859,818 to Goettl. In the system of U.S. Pat. No. 3,182,718, a single or common blower is employed to deliver either evaporatively cooled air or refrigerated air through the supply duct of the space to be cooled. Dampers are provided to recirculate air when the unit is used in a refrigeration mode of operation and to draw outside air through the unit when it is used as an evaporative cooler. In the evaporative cooler mode of operation, the air returned from the space to be cooled is exhausted into the atmosphere around the unit. The damper positions of the device shown in U.S. Pat. No. 3,182,718 are established by an electrically operated mechanical actuator to switch the air path from one which is suitable for a refrigeration unit to one which is suitable for operation as an evaporative cooler and vice-versa.
The Goettl U.S. Pat. No. 3,859,818 also is directed to a combination refrigeration and evaporative cooling air-conditioner. The unit of this patent has the refrigeration unit and the evaporative cooler unit located together in a single housing. Separate blowers are used for each unit. When the device is operated as a refrigeration unit, the normal air movement through the supply and return air ducts takes place. When the refrigeration unit is turned off and the evaporative cooler is turned on, a spring loaded damper is opened to cause the delivery of air from the evaporative cooler through both the delivery and return ducts of the refrigeration unit. Consequently, with the system disclosed in this patent, it is necessary to exhaust the air from the building through open doors, windows or other openings when the system is operated in the evaporative cooler mode.
Another approach to a combination refrigeration unit/evaporative cooler is disclosed in the U.S. Pat. No. 4,505,327 to Angle. This patent also discloses a custom composite interconnected refrigeration unit and evaporative cooler. When the system is operated as an evaporative cooler, the doors and windows may be closed. Air returned from the rooms of the building is returned through the return duct and is vented into the attic of the building in which the system is located. The system of the Angle Patent also utilizes the evaporative cooler unit to cool the condensor coils of the refrigeration unit when the refrigeration unit is operated to supply cooling air to the building interior. This condensor pre-cooling air then is vented into the attic of the building.
Two other patents which are directed to combination refrigeration units and evaporative cooler units, are the U.S. Pat. No. 3,252,508 to Goettl and U.S. Pat. No. 4,351,163 to Johannsen. The systems disclosed in these patents operate to use the same air supply ducts to supply cooled air into the building interior. In the evaporative cooler mode of operation, however, the return air duct is not used and it is necessary to exhaust the air out of the building through ceiling vents or open doors and windows in a conventional manner.
It is desirable to provide a simple and effective evaporative cooler unit which can be added onto pre-existing refrigeration air-conditioning units and which automatically switches over the duct work from the refrigeration mode to the evaporative cooler mode whenever one or the other of the blowers of these two systems is operated. It further is desirable to provide an evaporative cooler conversion unit which vents the return air outward into the atmosphere when the unit is operated in the evaporative cooler mode.